Hexagonal Planar [B 6 H 6 ] within a [B 6 H 12 ] Borate Complex: Structure and Bonding of [(Cp*Ti) 2 (μ-ɳ 6  : ɳ 6 -B 6 H 6 )(μ-H) 6 ].

Isolation of planar [B 6 H 6 ] is a long-awaited goal in boron chemistry. Several attempts in the past to stabilize [B 6 H 6 ] were unsuccessful due to the domination of polyhedral geometries. Herein, we report the synthesis of a triple-decker sandwich complex of titanium [(Cp*Ti) 2 (μ-η 6  : η 6 -B 6 H 6 )(μ-H) 6 ] (1), which features the first-ever experimentally achieved nearly planar six-membered [B 6 H 6 ] ring, albeit within a [B 6 H 12 ] borate. The small deviation from planarity is a direct consequence of the predicted structural pattern of the middle ring in 24 Valence Electron Count (VEC) triple-decker complexes. The large ring size of [B 6 H 6 ] in 1 brings the metal-metal distance into the bonding range. However, significant electron delocalization from the M-M bonding orbital to the bridging hydrogen and B-B skeleton in the middle decreases its bond strength.